1. Field of the Disclosure
The present invention relates to an arrangement, consisting of a metallic stent as a medical implant for treating lesions in blood vessels, and a packaging. The stent is arranged in a protected fashion in the interior volume of the packaging. The stent has a multiplicity of webs, which together form a tubular shape. The stent length and the stent lumen, as a passage, extend between the proximal and the distal end. The stent assumes a corresponding diameter in the dilated or released state. The stent surface is embodied in a hydrophilic fashion to promote hemocompatibility.
A special field of application is the vessel dilation in the field of percutaneous transluminal angioplasty, also including cardiovascular intervention. Such stents are together with a catheter, which is provided specially for this, inserted into the human body through a minimal opening, e.g. by puncturing an artery in the region of the thigh, and are moved up to the lesion, i.e. the vessel restriction to be treated, and are dilated there. Whereas the stent remains in the dilated blood vessel and supports the latter from the inside, the catheter is removed from the body. The flow of blood through the dilated and supported vessel is once again ensured. This process is carried out with the aid of instantaneous X-ray recordings, which on a monitor display both the blood vessels and the instruments inserted into the body.
Another special field of application is the treatment of aneurysms, i.e. dilated blood vessels. In this treatment, a stent graft—consisting of a supporting mesh and a cover—is inserted into the aneurysm in order once again to ensure the conventional blood flow.
2. Related Art
However, the metallic stents implanted into blood vessels harbor certain risks for the patient. Inter alia, thromboses can form at the structures of the stent. Combined with medicaments administered to the patient after the implantation, the occurrences of thromboses in the case of bare metal stents (BMS) could be reduced to less than 1% within the first 10 days. Nevertheless, this is one of the most-feared complications, particularly in the case of the coronary intervention.
A property of the stent that is desired by medical practitioners is the rapid growing in thereof, the so-called reendothelialization. The latter is of the utmost importance for the success of the stent therapy because the cells in this endothelial layer form essential antithrombotic factors. However, as long as the stent has not grown in, and the structures thereof are subjected to the blood flow, it is of the utmost importance to provide an antithrogenic stent surface.
It is well-known that stents with hydrophilic surface properties have a much higher hemocompatibility, i.e. a much lower thrombogenicity. Substances have been applied onto the stent surface by means of coating methods in order to increase the hydrophilicity on the stent surfaces [cf. Seeger J M, Ingegno M D, Bigatan E, Klingman N, Amery D, Widenhouse C, Goldberg E P. Hydrophilic surface modification of metallic endoluminal stents. J Vasc Surg. 1995 September; 22(3):327-36; Lahann J, Klee D, Thelen H, Bienert H, Vorwerk D, Hocker H. Improvement of haemocompatibility of metallic stents by polymer coating. J Mater Sci Mater Med. 1999 July; 10(7):443-8)].
By way of example, possible coating methods include “chemical vapor deposition” (CVD) or “physical vapor deposition” (PVD), by means of which materials, e.g. polymers or metals with defined layer thicknesses, are applied onto the stent surface. It was found that in the case of a polymer-coated BMS, the thrombocyte formation was reduced from 85% (BMS) to 20% (polymer-coated BMS) as a result of the increased hydrophilic properties of the surface.
On the one hand, strong friction forces acting on the stent surface occur during the clinical intervention; on the other hand, high mechanical stresses are generated on the surface of the individual stent webs during the expansion. After implantation, the stent is subjected to a permanent, pulsating load originating from the blood vessel. These high mechanical loads can result in a detachment of the coating, as a result of which there is a significant potential risk of thromboses, microemboli made of coating particles and serious chronic inflammations. Moreover, critical irregularities in the coating were even determined on yet to be implanted stents.
In addition to the mechanical influences, the stent coatings are damaged or broken down by the chemical reactions occurring in the body. Metallic coatings can corrode as soon as the differing electrochemical potential between coating and stent can be equalized via the battery effect by means of an electrolyte, e.g. blood.
Polymer coatings on stents are successively broken down by the body by means of enzymes. This process is often connected with an inflammation of the surrounding vessel cells, which cause undesired cell proliferations, which can lead to a re-narrowing (restenosis) of the blood vessel. Moreover, inflammations can already be caused by the polymer coating itself.
Although such surface modifications promote—as a positive effect—the growing in property of stents, they can however cause clinical complications due to the aforementioned problems. Until now no stent has been available with an optimum, hydrophilic surface that meets both the medical and the mechanical requirements.